Today, motor vehicle manufacturers are increasingly installing safety devices in vehicles to enable drivers to drive in a safer more efficient manner. For example, some manufacturers have included forward looking systems (FLSs), rear detection systems (RDSs) and side detection systems (SDSs) within certain vehicle models. An adaptive cruise control (ACC) system is one example of an FLS. The ACC system uses a radar sensor mounted at the front of the vehicle to detect objects in a forward path of the vehicle. If the lane ahead is clear, the ACC system maintains a set vehicle speed. However, when a slower vehicle is detected, the ACC system maintains a driver-selected distance using throttle control and limited braking between the vehicles. A typical ACC system uses mechanically scanned radar sensors, which normally improves the ability of the system to detect targets, e.g., vehicles in heavy traffic. A typical commercially available ACC system has a range of 150 meters and azimuth of 15 degrees and updates at a 10 hertz rate. An ACC system generally determines a range of a detected object, as well as the relative speed of the detected object.
SDSs detect objects that are at the side of a vehicle, e.g., in a driver's blind spot. A typical SDS includes a radar sensor that is mounted in each rear quarter panel of the vehicle. Each radar sensor is designed to detect objects in an adjacent lane. In this manner, the SDS can provide a visual indication to the driver to warn of objects in the driver's blind spot.
An example of an RDS is a back-up aid (BUA) or a reverse sensing system. BUAs are typically used as short range parking aids and include visual and audible alarms to warn a driver of an impending collision. A typical BUA system includes a radar sensor that provides a rear detection range of up to 6 meters. Some BUAs also include ultrasonic sensors that provide bumper coverage. A typical BUA is activated when a vehicle is: put into reverse gear and is useful for parking, parallel parking, backing in and out of parking spaces and backing at higher speeds.
Video systems are also increasingly being installed in motor vehicles. For example, one proposed BUA incorporates a camera in conjunction with ultrasonic sensors mounted in a bumper of a motor vehicle. In this system, a video display is positioned within the motor vehicle to allow monitoring of an area at a rear of the motor vehicle by a driver. That is, a rear facing camera is mounted at a back of a motor vehicle such that when the vehicle is placed in a reverse gear, a video display is activated to allow the driver to see obstacles which might not otherwise be visible. Such video systems have typically required a lens system that provides a relatively wide viewing angle in order to adequately cover an area at a rear of a motor vehicle. Unfortunately, wide-angle lens systems that provide low-distortion have tended to be relatively expensive and inexpensive wide-angle lens systems have tended to have a relatively high-distortion at a maximum field angle, e.g., forty percent distortion at a maximum field angle of fifty degrees.
What is needed is a wide-angle lens system that is relatively inexpensive and provides relatively low-distortion at a maximum field angle.